like here:
http://shub-hub.com/files/images/Screenshot-2.png

It might be QuArK floating point gayness but I know I found such edges on many maps. 

neg!ke just answered me:
qbsp bug, move the vertices or clip.
:) 

it's clip hull expansion logic. angled faces are expanded at an angle, and straight faces straight, so brushes that line up visually will end in different places after being expanded differing amounts on differing axes. 

visually inspect the player clipping hull by using the -hull 1 qbsp option. The map will probably look a bit different ... 

I just made the /^\ part 1 unit smaller on each side. Looks the same and got rid of the problem. Now that I think about it I simply could have made the one part a func_wall I guess. 

I thought (almost) all brush expansion problems were fixed in the most recent aguirre/tyrann tools... 

That fucked THF in some area, and I had to clip these corners... and it seems expansion problem are not completely solved... 

I used the clipping tool after doing some vertex editing and now I'm getting all kinds of errors with QBSP.exe whenever I try to compile.

So - what's wrong and is there any safer way to build a structure like this?:
http://i7.photobucket.com/albums/y259/msandt/vittua.jpg 

Clipping can cause alot of problems under the right circumstances - minor foibles of the various software that can mangle a map.

An important one in WC1.6a is that clipping across more than one brush in a window where those brushes are not adjacent causes it to crash - but not if you clip from a window where they're touching / stacked.

From the screenshot I'd say you need to rebuild the corner, but sticking to the grid; when you make the angle lock it to the grid as well - at 45 degrees. So all the brushes will have compass rose angles.

It an enclosed brush (not a wall against the void, ie. no leaks) so what errors is bsp giving - is it removing faces on any of the brushes?

Anyhow; the basic answer is rebuild it, hanging onto the grid for dear life - when cutting, scaling or whichever manipulation you make. 

A clarification - you don't need compass rose angles, just to snap to the grid size of your choosing. 32x2 or 16x2 in that case I reckon. 

Don't know what the fak is going on. I removed the structures (see the screenshot) and it still gives me shit. I removed some other crap I had recently built and still the program acts like a teenager. First it gives the usual "This program has encountered an error and will close" (QBSP.exe) Windows error message and then the compiling stops and tells me that a BSP file was not built. 

AguirRe's tooltips - just about every existing bsp error is listed in there.

http://user.tninet.se/~xir870k/ 

If you're using the default WorldCraft qbsp, then try one of my compilers and see if it helps. If you're already using one of them, I'd like to see that map file. 

Thanks - that just may have saved my map. I actually tried removing the whole area I had worked on today but even that didn't work. But these tools solved the problem and fixed a bunch of others as well (buttons not making a sound etc.). But I also noticed that some textures on curved surfaced got rotated 90 degrees. 

TxQBSP (recommended) or add the TreeQBSP option -oldaxis. 

I cannot believe how much headache this program is giving me - and I'm trying to build the last room. Now I can no longer select anything in 3D window. This actually has happened before but then I just restarted the program. Any ideas? 

This was a big problem for me to, but luckily Pope knew the answer on how to fix it. All you got to do is uncheck "Hardware Acceleration" in the options menu. You should now be able to click on objects in the 3d window after doing that. 

unfortunately it runs slow as shit without hw turned on. I still use 1.6, but I should probably switch to hammer :/ 

The transition from 1.6 to later versions is basically painless. All you have to do is make sure you know how to compile hl .map format into q1 .bsp format (say, using our modern compile tools). You'll have to get a q1 entity placement file working, as well. It's worth it! 

Okay, it works now.

Two questions:
-How to make monsterspawns so that stepping on a sector triggers the spawns?
-I tried using the portal texture that usually ends a level but it's not visible in game. 

1: Put monster into trigger_teleport, put tele_destination_something to where it should appear, make trigger_once for player to step into and target the trigger_teleport by it (eg trigger_teleport has targetname "montele1" and trigger_once has target "montele1").

2: trigger_teleport are invisible. Just create a new brush at the same place and give it the *TELEPORT texture to have it visible. 

1: Use Quoth, put monster where it should appear, set DELAYSPAWN flag on the monster, make trigger_once for the player to step into and target the monster by it (eg monster has targetname "montele1" and trigger_once has target "montele1").

@ Spirit: sorry ;-) 

Ha, actually I really second the suggestion to use Quoth. 

I'm not gonna use Quoth since I want this level to be accessible to everyone. The fact is that many casual usermap players are just too lazy to install any extra material just to play a usermap.

In WC, I noticed this thing called Default light level. Do mappers usually use this? 

But its an easy way to spoil a map if you set it too high - experiment until you get something you like.

It depends on the mood you want, typically set it so its less than your sunlight (which I'd advise using unless you don't have any sky brushes) with your actual pointlights being higher than that.

As I said before read aguirRe's documentation, there's alot of stuff to play with there, like anglesense, that can change the style of the map, only adding one (or a a handful of) variables to your worldspawn (SmartEdit).